The present invention relates to a catalyst activator, also referred to as a cocatalyst. More particularly the present invention relates to a cocatalyst particularly adapted for use in an addition polymerization process for polymerization of olefins. Such an activator is particularly advantageous for use in a continuous solution polymerization process wherein catalyst, catalyst activator, and at least one polymerizable olefin monomer are added to a reactor operating under polymerization conditions to prepare high molecular weight polyolefins.
It is previously known in the art to activate olefin polymerization catalysts, particularly such catalysts comprising Group 4 metal complexes containing delocalized π-bonded ligand groups, by the use of Bronsted acid salts capable of transferring a proton to form a cationic derivative of such Group 4 metal complex. Preferred Bronsted acid salts are such compounds containing a noncoordinating anion such as protonated ammonium, sulfonium, or phosphonium borate salts disclosed in U.S. Pat. Nos. 5,919,983, 5,198,401, 5,132,380, 5,470,927, and 5,153,157.
Additional activators for use as olefin polymerization cocatalysts activators include oxidizing materials including ferrocenium-, silver- and lead-salts of non-coordinating anions, especially perfluorinated borate anions, disclosed in U.S. Pat. No. 5,321,106 and elsewhere. Such compounds are also known to be useful in the synthesis of metal complexes through metal center oxidation, as disclosed in U.S. Pat. No. 5,189,192. Disadvantageously, however, because they are ionic compounds, such activators are extremely insoluble in aliphatic hydrocarbons and only sparingly soluble in aromatic solvents. It is desirable to conduct most polymerizations of α-olefins in aliphatic hydrocarbon solvents due to the compatibility of such solvents with the monomer and in order to reduce the aromatic hydrocarbon content of the resulting polymer product. Normally, ionic activators need to be added to such polymerizations in the form of a solution in an aromatic solvent such as toluene. The use of even a small quantity of such an aromatic solvent for this purpose is undesirable since it must be removed in a devolatilization step and separated from other volatile components, a process that adds significant cost and complexity to any commercial process.
Dietz, et al., J. Organometallic Chemistry, 1997, 545-546 pg. 67-70 disclosed the preparation of dialkyl substituted ferrocene compounds, in particular, dioctylferrocene. No attempt was made to form cationic derivatives from the organometallic compound.
Accordingly, it would be desirable if there were provided an oxidizing catalyst activator that could be employed in solution polymerizations that use an aliphatic solvent, including condensed α-olefin monomer. Additionally, it would be desirable if there were provided an oxidizing compound, especially an oxidizing salt of a perfluorinated borate anion for use in general metal complex syntheses employing an aliphatic solvent.